JPH04228329A - Central high-mount brake lamp of closed beam holography - Google Patents

Abstract

PURPOSE: To obtain a high mounted brakelight which will not reduce the effect even if it is small-sized and a light source is directed by optically coupling the light of a holographic brakelamp into a rear window by a prism to produce a holographic brakelight image that is visible from behind the vehicle by internal diffraction. CONSTITUTION: Playback illumination light is formed by a light source 115 and a filter 116, the light source 115 is connected to a brake lamp operating circuit, and when a brake pedal is stepped, the light source is energized. The output of the filter 116 is coupled into the lower part of a rear window by a prism 117 having the same spread in the longitudinal direction to the hologram structure 111. The angle of playback beam when it enters the rear window, the width W of the playback beam coupled into the rear window and the height H of the prism are selected to have a peculiar relationship to the thickness T of the rear window, so that the internally reflected light does not enter the intermediate plane of the prism/window.

Description

[Detailed description of the invention]

0001

FIELD OF INDUSTRIAL APPLICATION This invention relates to stereoscopic holograms illuminated by playback illumination light trapped in centrally mounted brake lights or brake lights for vehicles in general, and in particular in the rear window of a vehicle.
The present invention relates to a holographic central high-mount brake light device with a volume hologram).

0002

BACKGROUND OF THE INVENTION Federal regulations require motor vehicles to have central high-mounted brake lights in addition to conventional brake lights. Brake lights that can be mounted high are
It is intended to maximize the visibility of the brake lights to following drivers.

Central high-mount brake lights typically consist of a standard red transparent micro-convex lens and an incandescent light bulb contained within a fixed housing adjacent to the top or bottom of an automobile's rear window. (It is also relevant as a backlight in automobiles). The bulky housing, intended to prevent scattered brake light illumination from entering the driver's rear field of vision, partially reduces rear visibility, limits the design, and generally makes it unattractive. Not the point. Even though the bulky housing is intended to prevent scattered brake light illumination light from entering the vehicle, it is not very effective, especially if the backlight becomes dirty and/or covered with water vapor or snow. .

To avoid reducing the visibility of the bulbs and lenses, central high-mounted brake lights or holographic brake light systems have been developed in which a hologram fixed to the backlight of an automobile is illuminated by playback illumination light. Provides illumination for brake lights when illuminated. The hologram is nearly transparent to the driver's rear field of view, and the playback illumination source is outside such field of view, thereby avoiding reduced visibility caused by bulb and lens type brake light devices. . An example of a central high-mount holographic brake light system is
U.S. Patent No. 07/000,7 filed January 7, 1987
No. 93 and US Pat. No. 07,293,927, filed January 4, 1989.

Considerations for known holographic brake light systems that utilize projected playback illumination light include possible interference by those located at the rear of the vehicle and unwanted reflections from the rear window and from the light source. There is a possibility of unpleasant heat. Additionally, considerations for holographic brake light systems that utilize projected playback illumination include ambient lighting, including lighting that diffracts light into the rear field of view of the vehicle driver.

Another known holographic brake light system is disclosed, for example, in US Pat.
A fiber optic link, commonly described in US Pat. No. 4,892,369, couples the playback illumination light through the edge of the hologram. A consideration for edge-coupled systems is hologram efficiency, and highly collimated, very narrow bandwidth playback illumination, such as can be provided by a laser or very bright playback illumination light. It is light.

[0007]

SUMMARY OF THE INVENTION It would therefore be advantageous to provide a holographic brake light system that does not utilize projected playback illumination.

It would also be advantageous to provide a holographic brake light system that does not require excessively bright playback illumination light.

Another advantage would be to provide a holographic brake light system that does not require laser playback illumination.

[0010] These and other advantages include a three-dimensional hologram fixed to the rear window of a vehicle to produce brake light illumination in response to playback illumination, a prism optically coupled to the rear window, and a prism optically coupled to the rear window. According to the present invention, there is provided a brake light device for a vehicle, comprising a playback illumination light source for illuminating the vehicle.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Like elements are identified by like reference numerals in the following detailed description and in the figures of the drawings.

Referring now to FIG. 1, a holographic structure 111 is fixed to the inner surface of a rear window 113 of a vehicle.
1 schematically shows a side view of a confined beam holographic brake light comprising: FIG. The holographic structure 111 , which may include a transmission hologram or a reflection hologram, generates the brake light illumination light in response to the playback illumination light PB propagating to the holographic structure 111 through almost total internal reflection in the rear window 113 . do.

Playback illumination light is provided by a light source 115 and a filter 116 that provides an appropriate range of frequencies. The light source 115 is connected to the vehicle's brake light activation circuit and is energized when the brake pedal is depressed. The filter 116 can be a high pass filter or a narrow band filter, depending on the need for a sharp brake light image, which in combination with the light source 115 provides the appropriate luminous intensity according to the US brake light regulations. Provide spectral bandwidth.

As a specific example for a hologram where the hologram image is focused on the hologram plane, approximately 60
A high-pass filter with a cutoff wavelength of 0 nanometers (nm) would produce an image that would be perceived as red, and its apparent peak luminosity would be around 600 nm.
and 620 nm. For holograms where the hologram image is focused away from the hologram plane and there is a need for constant image sharpness, the optical spectral bandwidth needs to be lowered below that produced by a high-pass filter. Possibly, and a narrowband filter would be utilized.

The output of the filter 116 is a prism 117 that is longitudinally coextensive with the hologram structure 111 (ie, horizontally oriented in the car).
is coupled into the lower part of the rear window 113. Examples of light sources 115, shown schematically in FIG. 1 as a light bulb and a focusing lens, will be discussed further below.

The angle of the playback beam when it enters the rear window, the width W of the playback beam coupled into the rear window, and the height H of the prism have a specific relationship with the thickness T of the rear window. so that the inwardly reflected light will not be incident on the intermediate plane of the prism/window. For the brake light shown in FIG. 1, where the entire beam is utilized to illuminate the entire surface of the hologram structure 111, the parameters also define the position of the hologram structure as well as its maximum vertical dimension. In particular, the holographic structure can be positioned at a distance D from the upper edge of prism 117.

D=m*S

(Equation 1) where m is an integer and S is the difference between the point of entry of the ray into the rear window (a) and the point where the ray first hits the entrance surface after the first internal reflection (b). ie from the point of entry to the point of second internal reflection. Such a distance S can be expressed as follows.

S=(2T)/(tanθ)
(Equation 2
) where T is the thickness of the rear window and θ is the acute angle between the ray entering the rear window and the incidence surface of the rear window.

The maximum vertical dimension of the hologram will be S. This is because the entire hologram is illuminated by the entire inwardly reflected playback beam.

While the example shown in FIG. 1 shows the playback illumination light as being combined in the lower part of the rear window of the car, the playback illumination light could instead be as will be further shown herein. It can be combined in the upper part of the rear window with a light source located above the rear window.

Referring now to FIG. 2, there is shown a detailed view of an example of a hologram 111 embodied as a transparent stereoscopic hologram 51 superimposed on a support substrate 53. The laminar structure is fixed to the inner surface of the rear window 13 with a transmission hologram to the window surface. In operation, the playback illumination light incident on the hologram 51 by internal reflection within the rear window is not at the proper angle for diffraction, and therefore the substrate 53
pass to. The playback illumination light reaching the substrate 53 is
The hologram 51 is totally reflected inward at the intermediate surface of the substrate and at an appropriate angle for diffraction to produce the brake light illumination light.
is incident on the top.

Referring to FIG. 3, there is shown a detailed view of an example of a hologram 111 embodied as a reflective stereoscopic hologram 61 superimposed on a support substrate 63. The laminar structure is fixed to the inner surface of the rear window 13 with a reflection hologram against the window surface. In operation, playback illumination light is incident on the reflection hologram at an appropriate angle for diffraction to produce brake light illumination light.

The appropriate characteristics of the light source 115 are based on the playback characteristics of the stereoscopic hologram 111. In particular, since the playback illumination light propagates by internal reflection, the angle between the incidence of the hologram and the diffracted illumination light necessarily becomes large. As is well known for stereoscopic holograms, the angular bandwidth decreases as the angle between the incident illumination and the diffracted illumination increases. As a result, the hologram will be diffracted with relatively high efficiency only over a very narrow range of incidence angles in the plane of incidence defined by the normal to the hologram structure 111 and the central axis of the structure reference beam. As a particular example, such a plane of incidence can be chosen to be parallel to the plane of FIG.

From an efficiency standpoint, the playback illumination light incident on the hologram 111 is made into a fully collimated beam parallel to the plane of incidence. Hologram diffraction efficiency is less sensitive to changes in the angle of incidence in the direction perpendicular to the plane of incidence, so the playback illumination light incident on the hologram can be made relatively non-parallel in that direction, but the hologram is significantly diffracted by Collimation in a direction perpendicular to the plane of incidence results in blurring of the diffracted beam in the horizontal direction, where the unpleasant effect on the field of view of the brake light is minimal.

Referring now to FIG. 4, the hologram structure 11
A light source 115A is shown providing substantially collimated playback illumination light that is parallel to the plane of incidence for 1 . In particular, the light source 115A comprises a row of incandescent bulbs 211 with each filament being long and very thin, the long dimension of the filament being approximately parallel to the lower edge of the rear window portion closest to the bulb. Illumination light from the bank of incandescent bulbs 211 is focused by a suitable lens structure 213, such as a fly's eye spherical lens array configured with a spherical lens for each bulb. Alternatively, the lens structure 213 may comprise a cylindrical lens superimposed with a cylindrical lens array having lens groups rotated 90 degrees with respect to the cylindrical lens. The illumination light provided by lens structure 213 is transmitted through filter 116 of the structure of FIG.
is filtered by a filter 216 having characteristics as described above in connection with.

Referring to FIG. 5, a light source 115B is further shown providing substantially collimated playback illumination parallel to the plane of incidence on hologram 111. Light source 115B comprises an elongated filament tube 311 that is generally parallel to the lower edge of the rear window portion closest thereto. The illumination light from the array of filament tubes 311 is focused by a suitable lens, such as a cylindrical lens. lens 313
The illumination light provided by phytal 1 of the structure of FIG.
filter 316 having characteristics as previously described with respect to 16.

Referring now to FIG. 6, hologram 111
Another light source 115C is shown providing substantially collimated playback illumination light parallel to the plane of incidence on the light source 115C. Light source 115C is incandescent bulb 411 and bulb 4
11, the fiber is connected to the housing 417.
lens 4 for concentrating into a fiber optic bundle 415 disposed within the optical fiber bundle 415 providing a long narrow output section 419;
13. The output illumination light from the fiber optic output section 419 is provided by a suitable lens such as a fly's eye cylindrical lens array, a cylindrical lens, or a cylindrical lens superimposed with a cylindrical lens array as described above. Concentrated by 421. The illumination light provided by lens 413 is transmitted through filter 116 of the structure of FIG.
is filtered by a filter 416 having characteristics as previously described with respect to FIG.

The use of input coupling prisms allows for greater design flexibility, wider beams, and more efficient coupling of playback illumination light compared to edge coupling. In particular, edge bonding requires a very narrow beam and will not allow relatively smaller beam angles (compared to vertical).

relatively large with respect to the vertical line (for example 61
It is noted that coupling the playback illumination light into the rear window at an angle of incidence (greater than 100 degrees) provides the advantage of maintaining total internal reflection in the presence of water or ice on the rear window. Maintaining total internal reflection in the presence of dust and debris is achieved through the use of pyrolytics applied to the outer surface of the rear window for use with beam angles of approximately 73° or greater.
ic) can be achieved by a silicon diode layer.

Referring now to FIG. 7, a confined beam holographic brake light is shown in which the hologram is illuminated by multiple reflections of the playback beam. In other words,
The hologram is illuminated by horizontal stripes, each stripe corresponding to a respective internal reflection. Since the implementation of the multiple bounces of FIG. 7 relies on the playback illumination light not being diffracted on the path beyond the hologram where the hologram is disabled,
Playback illumination light is used more effectively.

The angle of the playback beam when it enters the rear window, the width W of the playback beam, and the height H of the prism are selected to have a specific relationship with the thickness T of the rear window. , the inwardly reflected light will not be incident on the prism/window intermediate plane, and the illumination fringes on the hologram will not necessarily overlap properly. Hologram structure 111
The hologram structure 111
will be located at any of the distances D defined by Equation 1 above for single-pass illumination systems, but also have a vertical dimension that is an integer multiple of the distance S defined above for Equation 2. be able to. In fact, the requirements can be relaxed somewhat. This is because the filament of the actual light source is not the true point of the source and therefore perfectly collimated illumination light is not provided.

Referring now to FIG. 8, there is shown a side view of another embodiment of the present invention that utilizes an overhead illumination source, ie, a source positioned above the rear window of a vehicle. The output of the halogen bulb 511 is reflected by a pseudo-elliptical reflector 513 to a cryogenic mirror 515 disposed on the top surface of a wedge-shaped glass substrate 517. A heat reflective metallization 519 is disposed on the bottom surface of the wedge-shaped glass substrate that is angled to reflect heat toward the heat sink 521 .

[0033] Pseudo elliptical reflector 513 and low temperature mirror 51
5 is formed such that the illumination light reflected by the cryogenic mirror 515 converges on a linear focal point at the entrance of the first acrylic light guide 523 . At the entrance of the light guide 523 , the width of the illumination beam perpendicular to the plane of the drawing should be at least the same as the width of the brake light hologram 111 , and the light guide 523 is dimensioned accordingly. Light exiting the first light guide 523 is directed into the entrance of the second acrylic light guide 524 . Especially the first
The exit surface of the light guide and the entrance surface of the second light guide are prismatic surfaces of suitable angles so that the refraction of the illumination light being coupled from the first light guide to the second light guide is properly directed into the light guide. Essentially, the prism surface functions to bend the illumination beam with minimal fanning.

High pass or narrow band pass filter 527
is placed at the exit of the second light guide 525 , and the output of the filter 527 is filtered by a prism 529 .
Thin layer structure 53 comprising a brake light hologram structure 111
1 is combined. As a specific example, the laminar structure includes first and second waterwhite glasses having a holographic structure supported therebetween.
) layer. The laminar structure is inserted into a suitably shaped notch formed in the upper part of the rear window.

Referring now to FIG. 9, there is shown an example of exposure equipment that can be utilized to record a brake light hologram structure 111 according to the present invention.

A holographic recording plate comprising a holographic recording layer 611 and a transparent support substrate 613 is constructed using an oil gate trough (oil gate trough) filled with a refractive index matching fluid.
opening 615 of gate through) 617
is supported within. In the example shown, the holographic recording layer comprises dichromate gelatin or a photopolymerizable compound. One side of the opening is a wedge-shaped prism 6
19 and one face 619a of the prism, and the recording layer is supported parallel to the face of such prism. Wedge prism 619 further includes a surface 619b forming an acute angle with surface 619a.

Oil gate trough 617 also includes an outer surface 417a that is parallel to a wedge-shaped prism face 619a forming one side of oil gate trough opening 615.

The exposure equipment further includes a lens array 623 of lenslets parallel to and separated from the oil gate trough surface 617a by an air gap.
Equipped with. In the example shown, the lenslet array 623 comprises a positive plano-concave cylindrical lens array 623a superimposed with a negative plano-convex cylindrical lens array 623b with its longitudinal axes at 90 degrees to each other. The plano-concave cylindrical lens array 623a is for vertically dispersing light, while the plano-convex cylindrical lens array is for horizontally dispersing light.

It should be understood that other forms of cylindrical lens arrays with orthogonally oriented longitudinal axes can be utilized for the lenslet array 623 of lenslets. For example, both cylindrical lens arrays can be positive or both negative. Also, the cylindrical lens arrays could be separated by air gaps, in which case a suitable anti-reflective coating would be utilized.

The respective collimated beams are utilized to generate a reference beam RB and an object beam OB. Preferably, such beams are emitted from the same laser source whose output is split by a beam splitter. The beam splitter output is made dispersive by respective dispersive optics such as an object lens and a pinhole aperture. Each dispersed beam is then collimated by a respective collimating optical element. The beam parallel to the reference beam is directed to the recording medium via prism face 619b at an angle appropriate to the intended playback geometry and which will normally be large as measured with respect to the vertical. be combined.

The beam parallel to the object beam is based on the required directivity of the diffracted playback illumination light and relative to the angular orientation of the rear window on which the hologram will be mounted. the lenslet array 621 at an angle deemed appropriate.

Referring now to FIG. 10, for recording a transmission stereoscopic hologram of a hologram structure 111 having a hologram recording film having the same orientation as the attached direction of the resulting stereoscopic hologram as shown in FIG. A side view of another exposure installation is schematically shown. For example, a holographic recording film 711 of dichromate gelatin supported by a glass substrate 712 is
It is exposed to an object beam OB and a reference beam RB, which are coupled to a film 711 by a prism 713 . The angle of incidence of the reference and target beams on the holographic recording film is determined by the desired playback geometry and the relationship between the recording and playback wavelengths.

The object and reference beams are preferably generated from the same laser source 712, the output of which is split by a beam splitter 715 to provide respective laser outputs for the object beams, such as a microscope objective and a pinhole aperture. The dispersive optics 717 are made to be dispersive. The dispersed illumination light provided by dispersive optics 717 passes through an iris 719 to a diffuser screen 721 with a mask 723 on its output side.
pass to. The masked output of diffusing screen 721 is focused by lens 725 whose output is directed into prism 713 .

The laser power for the reference beam RB is made to be dispersed by dispersive optics 727, such as a microscope objective and a pinhole diaphragm. Dispersive illumination light provided by dispersive optics is provided by the iris 72.
9 to a collimating lens 731 whose output is directed into a prism 713 .

The hologram structure 111 also includes a rainbow-like hologram that creates a real image floating behind the rear window and visible to drivers of following cars. A rainbow hologram diffracts incident light of any one wavelength into a very narrow vertically focused "slit" positioned in the eyebox and horizontally wide. Thus, with a broadband source such as an incandescent lamp, and without a band-limited filter, each wavelength is placed at a different height than that of the other wavelengths through a slit exit pupil.
pupil). The rainbow hologram would be designed so that the range of wavelengths useful for the brake light would be viewed over the required vertical angle. The position of the slit exit pupil will be designed to be positioned in the most appropriate position for drivers of following vehicles. This image becomes progressively blurred by transposing such positions back and forth. This is because the viewer will no longer look through a narrow slit exit pupil for each color.

To meet the color requirements of the brake light, a high pass filter 116 may be utilized as described above with respect to non-iridescent holograms. However, a rainbow hologram will provide an image with desirable sharpness as it is positioned away from the plane of the hologram.

Referring now to FIG. 11, hologram structure 1
Exposure equipment for making rainbow holograms for 11 is shown. A collimated beam passes from the laser, for example, through a spatial filter 811 to a focusing lens 813. The output of focusing lens 813 is incident on high gain screen 815. The output of high gain screen 815 is masked by a mask 817 with slit holes formed therein. The illuminated slit mask is the lens 819
to form a real image 835 at plane F. The output of lens 819 passes through a mask 821 and an image reticle 821, as an example of which may be transparent with the brake light image recorded in the hologram. The image output of the image reticle is formed by a glass substrate 8 supporting a recording medium layer 827, such as dichromate gelatin.
Pass through 25.

The recording medium layer 827 is a block prism 8
29 and separated therefrom by an index-matching oil in an oil gate trough, such as that described above with respect to the exposure equipment of FIG. The reference beam is coupled to the recording medium via the face of a block prism configured such that the reference beam is incident on the recording medium at an angle determined by the desired playback angle.

The reference beam passes through a spatial filter 831 whose output is made parallel by a parallel ray lens 833.
formed by passing a parallel beam through the

In the foregoing, a holographic brake light system is disclosed which advantageously utilizes playback illumination light and is prismatically coupled into the rear window of a vehicle for propagation by internal reflection. It avoids space usage limitations due to projected lighting and allows for a greater amount of playback illumination light to be produced than edge-illuminated systems. Additionally, the holographic brake light system disclosed herein is less sensitive to the surrounding environment than projection playback systems. .

Although particular embodiments of the invention have been described above, various modifications and changes therefrom will occur to those skilled in the art that depart from the scope and spirit of the invention as defined by the appended claims. can be executed without

[Brief explanation of the drawing]

FIG. 1 is a schematic side cross-sectional view of a confined beam holographic brake light system according to the present invention.

2 is a schematic side cross-sectional view illustrating the operation of the confined beam holographic brake light system of FIG. 1 implemented by a transparent stereoscopic hologram; FIG.

FIG. 3 is a schematic side cross-sectional view illustrating the operation of the confined beam holographic brake light system of FIG. 1 implemented by a reflective stereoscopic hologram.

FIG. 4 shows an example of a playback illumination source for the confined beam holographic brake light system of FIG. 1 comprising an array of incandescent lamps.

FIG. 5 illustrates an example of a playback illumination source for the confined beam holographic brake light system of FIG. 1 with a long thin filament tube.

FIG. 6 shows an example of a playback illumination source for the confined beam holographic brake light system of FIG. 1 comprising an incandescent lamp and an optical fiber for distributing light along a thin line.

FIG. 7 shows a confined beam holographic brake light system according to the present invention in which a confined playback beam passes through a stereoscopic hologram multiple times.

FIG. 8: The present invention utilizes an illumination source on the rear window of a vehicle and a light guide for coupling the illumination source to a coupling prism that couples the illumination into a substrate supporting a brake light hologram. FIG. 3 schematically illustrates another embodiment of a confined beam holographic brake light system according to the present invention.

FIG. 9 shows an exposure setup for recording holograms for the described confined beam holographic brake light system.

FIG. 10 shows another exposure setup for recording holograms for the described confined beam holographic brake light system.

FIG. 11 shows an exposure setup for recording reflective rainbow holograms for the described confined beam holographic brake light system.

[Explanation of symbols]

111... Hologram structure, 113... Rear window,
115, 115A, 115B, 115C... light source, 11
7,529,619,713,829...prism, 2
13,413,725,731,813,819...lens, 523,524,525...acrylic light guide,
611... Holographic recording layer, 711... Holographic recording film, 827... Recording medium layer.

Claims (18)

[Claims] 1. Illumination means for providing playback illumination light, and means for coupling the playback illumination light to a rear window by internal reflection for propagation therein, the coupled A light coupling means in which the thickness of the playback illumination light is greater than the thickness of the rear window, and a hologram for diffracting the internally reflected playback illumination light to produce a holographic brake light image that can be seen from the rear of the vehicle. A holographic brake light for an automobile having a rear window, comprising: 2. The holographic brake light of claim 1, wherein said optical coupling means comprises a wedge prism. 3. The holographic brake light of claim 1, wherein said hologram comprises a reflective hologram. 4. The holographic brake light of claim 1, wherein said hologram comprises a transmission hologram. 5. The holographic brake light of claim 1, wherein said hologram comprises a rainbow hologram. 6. The holographic brake light of claim 1, wherein said illumination means comprises an acrylic light guide. 7. The holographic brake light of claim 1, wherein said optical coupling means and said hologram are configured to substantially completely illuminate said hologram with a single pass of internally reflected playback illumination light. 8. The holographic brake light of claim 1, wherein said optical coupling means and said hologram are configured to substantially completely illuminate said hologram with multiple passes of internally reflected playback illumination light. 9. Illumination means for providing playback illumination light, and for coupling the playback illumination light to a rear window by internal reflection for propagation therein, the coupled a wedge-shaped prism in which the width of the playback illumination light is wider than the thickness of the rear window; and a hologram for diffracting the internally reflected playback illumination light to produce a holographic brake light image that can be viewed from the rear of the vehicle. and wherein the wedge prism and the hologram are configured to substantially completely illuminate the hologram with a single pass of internally reflected playback illumination light. Brake lights. 10. The holographic brake light of claim 9, wherein said hologram comprises a reflective hologram. 11. The holographic brake light of claim 9, wherein said hologram comprises a transmission hologram. 12. The holographic brake light of claim 9, wherein said hologram comprises a rainbow hologram. 13. The holographic brake light of claim 9, wherein said illumination means comprises an acrylic light guide. 14. Illumination means for providing playback illumination light, and for coupling the playback illumination light to a rear window by internal reflection for propagation therein, the coupled a wedge-shaped prism in which the width of the playback illumination light is wider than the thickness of the rear window; and a hologram for diffracting the internally reflected playback illumination light to produce a holographic brake light image that can be viewed from the rear of the vehicle. and wherein the wedge prism and the hologram are configured to substantially completely illuminate the hologram with a plurality of passes of internally reflected playback illumination light. Brake lights. 15. The holographic brake light of claim 14, wherein said hologram comprises a reflective hologram. 16. The holographic brake light of claim 14, wherein said hologram comprises a transmission hologram. 17. The holographic brake light of claim 14, wherein said hologram comprises a rainbow hologram. 18. The holographic brake light of claim 14, wherein said illumination means comprises an acrylic light guide.